Last April a prestigious small-scale hydropower plant in the western region of Bosnia and Hercegovina was connected to the grid. What makes run-of-river plant Glavica on the banks of the Vrbas stand out is its mechanical equipment.

Two structurally identical double-regulated Kaplan turbines by Voith Hydro are used to drive two modern synchronous generators, which are provided by long-standing manufacturer Hitzinger from Linz. In a normal year, the two machine combinations supply a total of 9.5 GWh of clean energy to the Bosnian power grid – a sizeable contribution to the country’s ambitious energy targets.

The facility that went on-line in Western Bosnia and Hercegovina last year is a real showcase example of modern hydropower utilisation: the Glavica hydropower plant – a project with an interesting history. More than 50 years ago, back when the country was still part of Yugoslavia, there were plans to build a hydraulic power plant at the same site, around two kilometres west of the city of Šipovo. These plans called for a 30 m high dam wall, which would have pushed the reservoir head back to where the Pliva river rises from two sources, around 5 kilometres away from the plant site. “This was where various measurements and geologic tests were conducted on both sides of the river. A 30 m exploratory tunnel from back then still exists today,” the operators of project firm BBB d.o.o. Šipovo told zek HYDRO. In 1954 a water measuring station was set up at the site. During the following decades regular detailed water measurements were taken. As BBB d.o.o. explain, these long-term sample data are rather more detailed than the measurements taken at other hydropower sites in the region. “These measurements showed that the Pliva river has one of the most steady discharge flow rates in all of Europe.

As environmentally compatible as possible
“The original project would have destroyed the site’s natural beauty up to the Pliva’s springs. So the idea with the 30 m barrage was dropped. After all, this stretch of the Pliva and the surrounding area are real natural treasures that enjoy a high level of protection, and deservedly so,” explains the spokesperson of BBB d.o.o., which is owned by the Lujic family. It was still before the breakup of Yugoslavia in the late 1980s that a new hydropower project at the same site was envisaged. This time the plan was to put up a small-scale hydropower plant with a 5 metre high transverse structure and an installed capacity of 0.97 MW. However, this plan, too, was never realised.
Next, the owners of BBB d.o.o., who are locals themselves, set about to develop their own concept, which was to enable a carefully balanced, environmentally friendly utilisation of hydropower. The ecosystem and natural beauty of the Pliva area were to be left undisturbed. “Design firm Encos of Sarajevo helped us to develop our initial concept draft further. This allowed us to preserve the landscape and ecosystem of the Pliva river and the surrounding area while achieving an even greater level of hydropower utilisation than projected in the plans from the 1980s,” explains BBB d.o.o’s spokesperson.. The firm had already been granted a permit for the Glavica site in 2006.

Performance boost over previous project
The proposed new solution included a 235 m longitudinal sill to divert the water flow near the left riverbank towards the hydropower plant. This version raised the performance to around 1.5 MW, clearly more than the previously planned solution. Eighteen smaller lateral sills along the right riverbank now enable fish to migrate undisturbed upstream and downstream. A further aspect of the concept concerned the construction work in the tailwater area. A 600 m stretch of the riverbed had to be cleared from decades’ worth of accumulated bedload. This would increase the net head by 1.5 m. Next, the project plan was presented to governmental representatives and ministers, who finally gave it their thumbs-up. The fact that it then took almost ten years to get all the required permits is due mainly to the relatively young administrative bodies to whom this type of approval process was still unknown territory.

Careful selection of suppliers
Financing was, of course a key element of the project, and one that was not to be left to foreign investors. As BBB d.o.o.’s spokesperson explains, “As far as financing was concerned, we were able to win domestic investors, who provided the necessary funds from their own resources and bank loans.” An aspect of particular importance to the project’s stakeholders was the matter of choosing the appropriate equipment for the facility. BBB d.o.o. had a clear policy: “As we had already gone to great lengths in our planning to keep everything eco-friendly and environmentally sound, we took great care in selecting suitable suppliers for the power plant equipment.  Apart from cost efficiency, our main requirements were long-standing experience and high manufacturing quality standards. Overall we invited twelve turbine manufacturers to the tender process. After careful deliberation we decided to have our small-scale hydropower plant equipped with the latest technical solutions from Voith Hydro. As for generator technology, we put our trust in the know-how of Hitzinger as our provider of choice.

Powerful yet compact
“To take full advantage of the hydrological conditions on the Pliva, the customer decided in favour of two vertical double-regulated Kaplan turbines,” recalls Voith Hydro’s project manager, Dipl.-Ing. Zijad Bajramovic. Apart from the turbines, the well-established turbine specialist also delivered the two Hitzinger generators and the entire hydraulic equipment. In addition, the Austrian hydropower specialist was also entrusted with the supervision of the installation and start-up precess. In the end, the Lower Austrian engineers were able to leverage their extensive know-how and underscore their well-deserved reputation as a competent, experienced hydropower engineering partner. This was confirmed by the project planners at BBB d.o.o., who stated that “We are very pleased to have chosen a turbine manufacturer who supported us with their technical solutions and expert assistance throughout the entire project implementation process.” One crucial aspect concerning the turbines’ design is their compact dimensions. “Protecting the environment was a key requirement, one that demanded the height of the power house to be kept to an absolute minimum. Meeting this criterion was possible mainly thanks to an extra-compact construction of the vertical Kaplan turbines,” explains Bajramovic. The turbines are specially designed, with the runner on a cantilevered generator shaft. By eliminating the usual bearing loss, this design improves the facility’s efficiency compared to a classic vertical Kaplan turbine arrangement. Where the turbine design was concerned, Voith’s engineers went for four-bladed Kaplan runners with a diameter of almost 1.6 m to ensure optimum utilisation of the water resources. “The main challenge was to simplify the manufacturing and installation processes while maintaining the high efficiency levels of the Voith hydraulics,” explains the manufacturer’s design engineer in charge, Jürgen Grill. As he points out, the entire machine concept was re-engineered to facilitate the installation process as much as possible.  Thanks to the new compact design it was possible to speed up the installation and concrete work, and as a result the overall implementation.

Custom-built machines
Each of the two machine units is designed for a gross head of 6.9 m  with a design flow rate of 14 m3/s, providing a rated output of up to 813 kW. Running at a rotational speed of 273 rpm, each of the two structurally identical turbines drives a modern, powerful Hitzinger generator. The three-phase generators provided by high-profile manufacturer Hitzinger of Linz, are each designed for a rated output of 1,000 kVA. Reliability and performance are not the only qualities that make Hitzinger’s generator technology stand out. An essential strength of the generators lies in the fact that they are no ‘off-the-shelf’ products. On the contrary: Hitzinger’s generators are custom designed and manufactured to meet the customer’s needs and operational conditions. Every-thing is custom-built, from the machine’s magnetic design to its insulation system. In this respect Hitzinger have always kept to the motto, “Better design conservatively.” As a result, the machines come with extra capacity reserves built in – which distinguishes them from other industrial generators that are constantly operated at their capacity limit. One of the most significant advantages is Hitzinger’s in-house software, which has been refined over decades. They are optimised to enable the engineers to design the required machines with a high level of precision and speed.

9.5 GWh of clean energy per year
One unique characteristic of the Glavica hydropower plant is its relatively low design flow level. This means that the ratio of the turbines’ design flow rate to the Pliva’s average water flow rate is relatively low, which translates into a high efficiency level. On average, the machines are running under full load on 100 days per year, resulting in an overall utilization of the water resources of around 85 percent. Says Zijad Bajramovic, “Thanks to the relatively flat discharge line of the Pliva river, it is possible to operate one machine unit under full load on an average 260 days per year.” With the project completed, the project developers at BBB d.o.o. Šipovo can look back on a satisfying experience: “The construction of hydropower plant Glavica has taken a lot of cost and effort to complete. But in the end we were able to put up a beautiful facility, so it was all worthwhile.” In a normal year, the new run-of-river plant generates around 9.5 GWh or clean power, enough to provide more than 2,700 average households in Bosnia and Hercegovina with energy. As a result, the hydropower plant not only helps to raise the share of renewables in the Balkan country to the planned level. It also contributes to the overall expansion of hydropower, which is to replace coal-fired energy in the long run. However you look at it, Glavica is a model facility.